RESUMEN
Ni(II) complexes bearing an o-bis(aryl)phosphinophenolate ligand were synthesized as catalysts for copolymerization of ethylene and alkyl acrylates. When the P-bound aryl group was 2,6-dimethoxyphenyl group, one of the oxygen atoms in the methoxy groups coordinated to the nickel center on its apical position. This complex was a highly active catalyst without any activators to give highly linear and high molecular weight copolymers. The structures of the copolymers were determined by 1H and 13C NMR to clarify that the alkyl acrylate comonomers were incorporated in the main chain and that the structures of the copolymers were significantly influenced by the structure of the aryl group in the ligand.
RESUMEN
A triphenylphosphine-catalyzed cyclization of alpha-keto esters, alpha-keto nitriles, or alpha,alpha,alpha-trifluoroacetophenone with dimethyl acetylenedicarboxylate is reported to produce highly functionalized alpha,beta-unsaturated gamma-butyrolactones in moderate yields. Thus treating a mixture of methyl 4-nitrophenylglyoxylate and dimethyl acetylenedicarboxylate with 20 mol % of triphenylphosphine afforded 5,5'-disubstituted 3-methoxy-4-(methoxycarbonyl)-2(3H)-furanone in 94% yield. In the reaction of alpha-keto esters R(1)COCOOMe, an electron-withdrawing R(1) substituent is required for satisfactory reactivity. On the other hand, electron-donating R(1) substituents give higher yields with alpha-keto nitriles R(1)COCN. Another electron-deficient carbonyl compound, alpha,alpha,alpha-trifluoroacetophenone, gave the corresponding lactone in good yield. The use of an alpha-hydroxy ketone as an electrophilic carbonyl compound with more than 1 equiv of triphenylphosphine produced dihydrofuran derivatives. One equivalent of triphenylphosphine oxide was obtained as a major product. An intramolecular Wittig reaction is proposed as a reaction mechanism.
